This invention relates to a method of manufacturing arc tubes, particularly to improvements in the manufacture of arc tubes of metal halide lamps suitable for use as light sources of motor vehicle headlamps, among other applications.
Arc tubes for use as light sources of vehicular headlamps are, as the name implies, fairly short tubes of vitreous material containing two electrodes as well as chemicals such as mercury and metal halides. For the manufacture of high performance arc tubes, it is essential that the electrodes and the chemicals be introduced into the vitreous tubes without being contaminated by the atmospheric air.
Conventionally, for the attainment of this objective, there were first prepared semifinished arc tubes by inserting one electrode into one end of each vitreous tube and by sealing this end of the tube. Then the other ends of the semifinished arc tubes were inserted respectively in nozzle assemblies depending from a rotary index table. Then, with the semifinished tubes filled with an inert gas, typically argon, through conduits coupled right-angularly to the nozzle assemblies, the chemicals and the other electrodes were introduced into the semifinished tubes through the nozzle assemblies.
This conventional practice is objectionable because the passageways of the chemicals and the electrodes into the semifinished tubes through the nozzle assemblies are only partly filled with argon. The chemicals and the electrodes were left exposed to the atmospheric air both before, and halfway during, their introduction into the semifinished tubes.